Ask any fish freak - we know, or think we know, that our fish have personalities. Who could miss them? Some are aggressive, others are docile; some are bold, others are shy.

In some circles, ascribing personalities to animals is still a cardinal sin of biology and warrants being branded with a scarlet A (for anthropomorphism). Nonetheless, scientists have consistently found evidence of personality traits in species as closely related to us as chimpanzees, and as distant as squid, ants and spiders.
A recent study in Animal Behaviour has looked at developmental processes resulting in shy/bold animals. David Sinn, Samuel Gosling, and Natalie Moltschaniwskyj have measured the behaviour of dumpling squid, Euprymna tasmanica, in two tests, a threat and a feeding test, at five times across their life span. The results showed that how squid behaved in the threat test was not related to their behaviour in the feeding test. However, squid did show a consistent behavioural response within a test over time.
The experiment also showed that different phenotypes (i.e. bold versus shy individuals) displayed different amounts of developmental variation. Shyer animals were more plastic in feeding tests, while bolder animals were more plastic in threat tests. These results suggest that for some animals shy/bold behaviour throughout development is uncorrelated across different tests situations related to risk, while within a test situation, there may still be developmental constraints to changing shy/bold behaviour.

For more information, see the paper: Sinn, D.L., Gosling, S.D., Moltschaniwskyj, 2008. Development of shy/bold behaviour in squid: context-specific phenotypes associated with developmental plasticity. Animal Behaviour, 75, 433-442.